Integrated optical system for endoscopes and the like

ABSTRACT

Optical systems for endoscopes, borescopes, dental scopes, and the like which are characterized by having three groups of lenses of positive optical power and an external entrance pupil. Typically, all three groups of lenses are displaced from the pupil and focal planes. As a consequence, the displaced groups take part in the image transfer as well as in the pupil transfer. The optical power requirements can thus be shifted from one group to another, distributing as well as reducing the overall power requirement. Moreover, the aberration correction can also be shared between these groups. The first group, which conventionally has the highest optical power, and consequently a large amount of aberrations to be corrected, can in this way transfer some of the optical aberration correction to the other groups. The sharing of the optical functions and aberration correction results in a fully integrated optical system. The reduction in the total amount of optical power is so large that a line-of-sight deviating prism can be readily accommodated between the entrance pupil and the first lens group. The resulting simplicity of the optical system makes it suitable as a disposable item.

This is a continuation application of U.S. patent application Ser. No.08/687,910, filed Jul. 26, 1996, which issued as U.S. Pat. No.5,841,578, which is a continuation of U.S. patent application Ser. No.08/351,481, filed Dec. 6, 1994, which issued as U.S. Pat. No. 5,633,754,both which are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to optical lens systems, andmore particularly to lens systems suitable for endoscopes and the like.

BACKGROUND OF THE INVENTION

In endoscopy and related fields, such as borescopes and dental scopes,the complete optical system is thought of as consisting of four basicand separate optical functions. Those functions are, in sequence of thedirection of the travelling light, as follows:

1. an objective which forms the first image of an object undersurveillance,

2. a field lens which images the pupil of the objective onto the nextimage transfer lens,

3. an image transfer lens which reimages the first image onto the nextfield lens. The pupil and image transfer steps are repeated as often asis needed to obtain a desired tube length, and

4. a focussing lens which presents the final image to a sensor, like aperson's eye, a CCD camera, or a photographic film.

This approach is the classical approach, and it is appropriate for thefollowing reasons:

1. The design of the optical system is broken up into parts with singleand clearly defined and separate functions, functions to each of whichan optical designer may bring considerable experience, and

2. The light transfer capacity and information transfer capacity of anendoscope is at a maximum when the optical power is concentrated at theimage planes and pupil planes. The expedience of this approach isbrought out by numerous

U.S. patents on endoscopes which consistently treat the objective, therelay system, and the eyepiece as separate parts of the total system.

The disadvantage of treating the different optical components asseparate entities is that the distribution of the optical powers is veryuneven and that certain aberrations are naturally at a maximum, likeastigmatism, field curvature, and chromatic aberrations. The correctionof these aberrations require relatively short radii. These short radiiare difficult to fabricate, require tight tolerances, and they aretherefore the main contributors to the considerable cost of thefabrication of an endoscope. A truly inexpensive endoscope, sufficientlyinexpensive to be offered as a disposable item, is presently notpractical with conventional designs.

SUMMARY OF THE INVENTION

The present invention provides an integrated optical system suitable forendoscopes, borescopes, dental scopes, and the like which contains aminimum of elements and which elements have relatively long radii andneed not be of a meniscus shape. The outside entrance pupil location isvery suitable for a tapered probe or for concealment. The entrance pupildistance sufficient to accommodate a line-of-sight deviating prism is anatural consequence of the arrangement of the optical groups. The systemleads itself to mass production and is highly insensitive to tilt anddecentration of its components. As a consequence it is eminentlysuitable as a disposable item.

Broadly, the foregoing advantages are achieved in a lens system which ischaracterized by an integrated design which has an external entrancepupil and in which the majority of the groups are displaced from theimage planes and pupil planes. In this way most components share in thepupil transfer as well as in the image transfer. Moreover, theaberration correction is distributed in an advantageous way over all thegroups, providing relief to the first group which conventionally is inneed of most of the aberration correction. It has been found that thisintegration of the optical functions and aberration correction is verybeneficial in that it greatly simplifies the optical system.

A plano-convex lens, or even a double convex lens when used according tothe invention can be corrected for astigmatism since it is displacedfrom the stop location. In this way no optical surfaces of very shortradii are needed to correct the astigmatism of the total optical system.Furthermore, the spherical aberration of a convex-plano lens used in thepresent invention is very near the minimum possible for a singleelement. Also the chromatic aberration is greatly reduced by thedisplacement of the elements from the image planes and pupil planes as acomparison with the classical arrangement will readily show. A factortwo to four in the reduction of the chromatic aberration is thusachieved without the presence of a chromatic aberration reducingelement, sometimes making further color correction unnecessary. Even asystem incorporating several transfers is fully color corrected by theuse of a single color correcting element. The distortion, which isusually very high in the objective, is corrected at more convenient andeffective places. The result is a single integrated system whichreplaces the three conventional separate parts, i.e. the objective, thefield lens, and a relay lens. This single integrated system may beaugmented, as is well known in the art of optical design, withadditional optics, like a close-up lens, a field expander, a fieldflattening lens, or with additional relay groups, without fallingoutside the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical schematic view of an endoscope constructed inaccordance with a conventional layout in which each component has asingle function in the system.

FIG. 2 is an optical schematic view of a first preferred embodiment inwhich the entrance pupil is located outside the first group by arelatively small distance.

FIG. 3 is an optical schematic view of a second preferred embodiment inwhich full advantage of the power reduction and aberration reduction istaken by locating the entrance pupil outside the first group by a largedistance.

FIG. 4 is an optical schematic view of a third preferred embodimentwhich incorporates a rod-shaped element.

FIG. 5 is an optical schematic of a fourth preferred embodiment of allglass elements which incorporates a single negative element whichprovides chromatic aberration correction of the whole system.

FIG. 6 is an optical schematic of a fifth preferred embodiment of asimple glass & plastic system with full correction of chromaticaberration.

FIG. 7 is an optical schematic view of a sixth preferred embodiment inwhich the three basic groups have been augmented by an element near thefocal plane of the first group.

FIG. 8 is an optical schematic view of a seventh preferred embodiment inwhich a fourth element of low optical power has been added near thefocal plane of the first group and which contains a single negativeelement for correcting the chromatic aberrations.

FIG. 9 is an optical schematic of an eighth preferred embodiment whichincorporates a meniscus shaped element.

FIG. 10 is an optical schematic view of a ninth preferred embodimentwhich incorporates a second image relay and is fully corrected forchromatic aberrations with a single element of negative optical power.

FIG. 11 is an optical schematic view of a tenth preferred embodimentwhich incorporates a third image relay and is still fully corrected forchromatic aberrations using only one element of negative optical power.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The illustrative embodiments to be described below are standardized to alength of about 100 millimeters of the basic optical system and mostlyfor a nominal magnification of unity. In this way the performance of thevarious examples can be conveniently compared. Embodiments with othermagnifications, field of views, numerical apertures, and with additionalrelays are presented in order to show that the general concept of theinvention is effective over a wide range of applications. Theembodiments use conventional, non-GRIN (graded refractive index) lenselements, and thus each lens has a uniform refractive index. In FIGS. 1through 11 the object and image planes are indicated by an ‘O’ and ‘Im’,respectively and the pupil planes by a ‘P’. The optical system featuresof object plane, pupil plane, lens surfaces and final image plane arenumbered sequentially. Table I through XI present the constructionalparameters of the preferred embodiments illustrated in correspondingFIGS. 2-11 and the prior art embodiment illustrated in FIG. 1. Alldimensions are in millimeters. The first column indicates the surfacenumber shown in the figures, the second column indicates the radii, andthe third column indicates the axial separations. The refractive indicesand dispersion are presented in the usual manner, with respect to the e,F′, and C′ spectral lines. The aspheric data are presented in thestandard manner. The surface and plane numbers refer to those in thefigures. Table I refers to the system shown in FIG. 1, Table II to thesystem of FIG. 2, and so on for the other tables and figures.

FIG. 1 is an optical schematic of an endoscope which is constructed inaccordance with the classical concept of separation of the variousfunctions. Group I is an objective which contains the entrance pupilplane while group II represents a field lens which is located at thefocal plane of the objective. Group III represents a transfer lens whichtransfers the image formed by the objective unto a next focal plane. Allgroups are located at pupil planes or focal planes. It is apparent fromthe drawing as well as from the data of Table XII that the distributionof optical power is very uneven. The value of the sum of the absolutevalues of the curvatures, which is a measure of difficulty offabrication, is listed in Table XII for this version which isuncorrected for chromatic aberrations. A version corrected for chromaticaberration would have more than double the value for the sum of thecurvatures. The pertinent performance data are listed in Table XII andthe constructional parameters are listed in Table I.

FIG. 2 is an optical schematic of an endoscope of extreme simplicity.Only three plastic elements on non-meniscus shape and devoid of steepcurves are needed to provide diffraction limited performance for themonochromatic aberrations. Many applications do not require aline-of-sight deviating prism and in such cases a pencil-shaped tip,which is often an advantageous configuration, can be readily provided.The pertinent performance data are listed in Table XII and theconstructional parameters are listed in Table II.

FIG. 3 is an optical schematic of an endoscope which is also extremelysimple in construction but is nevertheless highly corrected for allaberrations, including chromatic aberrations. Although no negativeelement has been added to correct chromatic aberration, the chromaticaberration is more than a factor four smaller than in the classicallayout (c.f. FIG. 1) and is within the diffraction limit. This exampleclearly shows the advantage which a redistribution of power, with theattendant shift of pupil (P_(int)) location, brings. This somewhatextreme case is achieved at the cost of larger optical components.

FIG. 4 is an optical schematic of an endoscope which consists of onlytwo components. The second and third groups are cemented to a rod-shapedelement, so that there are only four glass/air surfaces. Despite itssimplicity, all aberrations are at the diffraction limit. This exampleshows that rod-shaped elements can be profitably employed in the presentinvention. It also shows that rod-shaped elements may alter the locationof the intermediate pupil plane (P_(int)) and focal plane of theobjective, which have now moved beyond the third and second groups,respectively. A shorter rod-shaped element can put the intermediatefocal and pupil planes (P_(int)) at the second (II) or third (III)element if so desired. The exemplary embodiments do not requiremeniscus-shaped optical elements. This does not, of course, precludetheir use, as is shown in this example. The gain in using meniscusshapes, however, is modest.

FIG. 5 is an optical schematic of an endoscope which is entirelyconstructed of glass elements, none of which are of the meniscus shape.All curvatures are shallow and of a spherical shape only. The firstgroup provides without any strain the needed space for a line-of-sightdeviation prism between the entrance pupil and the first group, even inthe case of a large field of view of seventy degrees. It is important tonote that, despite the fact that the first group is not color correctedin any way, the chromatic aberrations of the whole system are fullycorrected by means of a single negative element only. All three groupsare far removed from the intermediate image plane and the pupil plane,showing the full integration of the three groups. The pertinentperformance data are listed in Table XII and the constructionalparameters are listed in Table V.

FIG. 6 is an optical schematic of an endoscope which is partlyconstructed of glass and partly of plastic. Again no steep curves normeniscus elements are needed to achieve the relatively high N.A. of0.025. The distortion is well corrected. The object distance has beenset at infinite distance to show that the basic design is not affectedby a change in magnification as is generally the case with endoscopes.The pertinent performance data are listed in Table XII and theconstructional parameters are listed in Table VI.

FIG. 7 is an endoscope to which one more groups of optical power havebeen added, resulting in a modestly improved monochromatic performance.The added element is positioned close to the image plane of theobjective where it is most effective. Its relative weak, in this casepositive, power shows that most of the burden of the optical functionsas well as the aberration correction is carried by the groups which aredisplaced from the image planes and pupil planes. This example showsthat an additional element near an image plane or a pupil plane is notexcluded. The pertinent performance data are listed in Table XII and theconstructional parameters are listed in Table VII.

FIG. 8 is a highly corrected endoscope of all plastic elements with arelatively high N.A. of 0.025. Only one of the elements, the secondelement, favors a position which is close to an image or pupil plane butis again of low optical power. The pertinent performance data are listedin Table XII and the constructional parameters are listed in Table VIII.

FIG. 9 is an endoscope of similar design as the one shown in FIG. 8. Themagnification has been increased to 2×, showing that the design remainsvery similar to the 1× and 0.0× designs, as is generally the case withendoscopes. Again a meniscus element has been employed to show thatdespite the fact that the present invention can be very well executedwith non-meniscus elements, their employment is by no means excluded. Inthis case the fourth group, the meniscus element is of negative power,again showing that the fourth element is a non-essential addition to thethree group concept of the invention. The pertinent performance data arelisted in Table XII and the constructional parameters are listed inTable IX.

FIG. 10 is an endoscope to which a second relay has been added. It has avery large field of view of eighty degrees and a relatively high N.A. of0.025. Despite these large values a deviation prism can be readilyaccommodated in between the objective and the entrance pupil. The totalsystem is still very well corrected and needs only a single colorcorrecting element of low power in order to provide full correction ofthe chromatic aberrations. As the first three groups are fullycorrectable by themselves, the addition of classical relays to thosefirst three groups is not excluded. The pertinent performance data arelisted in Table XII and the constructional parameters are listed inTable X. Note that the second relay is different from the first relay.The number of curved optical surfaces in the second relay is differentthan the number of curved optical surfaces in the first relay.

FIG. 11 shows an endoscope with three image relays and is still verywell corrected. Again the chromatic aberrations are fully corrected witha single element of negative optical power. In this case the opticalpower of the color correcting element approaches a value comparable tothose of the other components. All elements are of glass and no asphericsurfaces are employed. The pertinent performance data are listed inTable XII and the constructional parameters are listed in Table XI. Notethat the second relay is different from the first relay. The number ofcurved optical surfaces in the second relay is different than the numberof curved optical surfaces in the first relay.

It is thus evident from these embodiments that the integration of thethree groups of which a conventional endoscope exists, the objective, afield lens, and a relay lens, greatly reduces the overall powerrequirement. The reduction in the overall power requirement naturallyreduces the amount of aberrations to be corrected which results in aconsiderable simplification of the optical system. An additional, and inmany cases a very valuable, feature is that the optimal location of theentrance pupil is outside the system.

TABLE I SURF RD TH INDEX v-VALUE CC 0 6.51 OBJECT PLANE 1 −.51 ENTRANCEPUPIL PLANE 2 2.60 1.40 1.4938 57.0 −52.0 3 −1.60 3.00 AIR −7.5 4 4.003.00 1.4938 57.0 −12.0 5 −3.80 33.00 AIR 6 18.00 2.00 1.4938 57.0 7−24.76 51.64 AIR 8 IMAGE PLANE EFL = −5.518 .020 N.A. 60 DEG F.O.V. MAGN= 1.000

TABLE II SURF RD TH INDEX v-VALUE CC 0 6.00 OBJECT PLANE 1 .60 ENTRANCEPUPIL PLANE 2 infinity 1.2 1.4938 57.0 3 −1.10 7.4 AIR −.40 4 infinity1.5 1.7762 49.3 5 −6.30 36.80 AIR 6 infinity 1.50 1.4938 57.3 7 −11.81 44.85 AIR −3.00 8 IMAGE PLANE EFL = −5.543 .020 N.A. 60 DEG F.O.V. MAGN= 1.000

TABLE III SURF RD TH INDEX v-VALUE CC 0 6.00 OBJECT PLANE 1 6.00ENTRANCE PUPIL PLANE 2 infinity 3.00 1.4938 57.0 3 −4.7   51.30 AIR −.654 25.70 7.00 1.4938 57.0 5 −11.70   18.00 AIR −2.90 6  7.00 2.00 1.493857.0 7 −13.48   6.72 AIR −560.00 8 IMAGE PLANE EFL = −3.216 .020 N.A. 60DEG F.O.V. MAGN = 1.000

TABLE IV SURF RD TH INDEX v-VALUE CC 0 6.00 OBJECT PLANE 1 2.00 ENTRANCEPUPIL PLANE 2 −5.00 1.80 1.4938 57.0 3 −2.10 1.70 AIR −.56 4   5.83 2.001.6203 63.1 5 infinity 48.00 1.8126 25.2 6 infinity 2.00 1.4938 57.0 7−7.01 36.50 AIR −1.30 8 IMAGE PLANE EFL = −4.846 .020 N.A. 60 DEG F.O.V.MAGN = 1.000

TABLE V SURF RD TH INDEX v-VALUE CC 0 6.00 OBJECT PLANE 1 .20 ENTRANCEPUPIL PLANE 2 infinity 3.00 1.7162 53.2 3 infinity 1.50 1.7762 49.3 4−4.0   .20 AIR 5 13.50 1.50 1.7762 49.3 6 −13.50   9.50 AIR 7 infinity1.50 1.7762 49.3 8 −10.9    30.80 AIR 9 infinity 1.20 1.8097 30.2 10  8.80 2.00 1.5914 61.0 11  −8.47 42.55 AIR 12  IMAGE PLANE EFL = −5.495.015 N.A. 70 DEG F.O.V. MAGN = 1.000

TABLE VI SURF RD TH INDEX v-VALUE CC 0 infinity OBJECT PLANE 1 3.2ENTRANCE PUPIL PLANE 2   4.90 2.5 1.4938 57.0 −1.50 3 −2.90 18.60 AIR−2.50 4 infinity 2.00 1.4938 57.0 5 −8.80 24.00 AIR −.70 6 −7.00 1.201.5901 29.6 1.40 7 infinity 2.00 1.6543 58.3 8 −6.55 40.51 AIR 9 IMAGEPLANE EFL = −7.794 .025 N.A. 60 DEG F.O.V. MAGN = .000

TABLE VII SURF RD TH INDEX v-VALUE CC 0 6.00 OBJECT PLANE 1 1.90ENTRANCE PUPIL PLANE 2 infinity 2.50 1.4938 57.0 3 −2.00 2.70 AIR −.66 4infinity 2.00 1.4938 57.0 5 −16.80  25.00 AIR 32.00 6 infinity 2.001.4938 57.0 7 −9.60 31.20 AIR −1.20 8 infinity 2.00 1.4938 57.0 9−17.85  24.68 AIR −28.00 10  IMAGE PLANE EFL = −5.301 .020 N.A. 70 DEGF.O.V. MAGN = 1.000

TABLE VIII SURF RD TH INDEX v-VALUE CC 0 6.00 OBJECT PLANE 1 3.20ENTRANCE PUPIL PLANE 2 infinity 2.50 1.4938 57.0 3 −2.50 3.00 AIR −.64 4infinity 2.00 1.4938 57.0 5 −26.00   24.70 AIR 57.00 6 infinity 2.001.4938 57.0 7 −9.20 25.00 AIR −1.00 8 −4.30 1.20 1.5901 29.6 −.30 9infinity 2.00 1.4938 57.0 10  −3.61 28.35 AIR −.70 11  IMAGE PLANE EFL =−5.599 .025 N.A. 60 DEG F.O.V. MAGN = 1.000

TABLE IX SURF RD TH INDEX v-VALUE CC 0 3.00 OBJECT PLANE 1 2.40 ENTRANCEPUPIL PLANE 2 12.40 3.00 1.4938 57.0 3 −2.32 9.70 AIR −.80 4 −7.60 2.001.4938 57.0 5 −8.10 15.90 AIR 2.80 6 infinity 2.00 1.4938 57.0 7 −10.0028.50 AIR −1.20 8 −24.00 1.20 1.5901 29.6 70.00 9 5.00 2.50 1.4938 57.010  −6.36 29.82 AIR 11  IMAGE PLANE EFL = −4.891 .025 N.A. 60 DEG F.O.V.MAGN = 2.000

TABLE X v- SURF RD TH INDEX VALUE AD AE 0 8.00 OBJECT PLANE 1 .10 EN-TRANCE PUPIL PLANE 2 infinity 3.80 1.8126 25.2 3 infinity 1.80 1.776249.3 4 −4.30 .20 AIR 5 11.40 1.50 1.7762 49.3 6 −17.00   10.00 AIR 7infinity 2.00 1.7762 49.3 8 −18.90   40.30 AIR 9 13.00 2.00 1.8550 23.610   8.50 2.50 1.4985 81.2 11  −19.30   39.80 AIR 12  infinity 2.001.7762 49.3 13  −8.34 20.00 AIR 14  infinity 2.00 1.7044 29.8 15  −8.8314.04 AIR 9.0E − 4 112.0E − 5 16  IMAGE PLANE EFL = 3.792 .025 N.A. 80DEG F.O.V. MAGN = −.500

TABLE X SURF RD TH INDEX v-VALUE 0 12.00 OBJECT PLANE 1 .10 ENTRANCEPUPIL PLANE 2 infinity 4.50 1.8126 25.2 3 infinity 2.00 1.7762 49.3 4−4.30 .20 AIR 5 38.00 1.50 1.7762 49.3 6 −14.00   15.00 AIR 7 infinity1.60 1.7762 49.3 8 −14.00   27.00 AIR 9 50.00 1.20 1.8550 23.6 10   4.503.00 1.4985 81.2 11  −4.70 28.80 AIR 12  infinity 2.00 1.7762 49.3 13 −11.00   26.70 AIR 14  infinity 2.00 1.7662 49.3 15  −9.90 27.30 AIR 16 −14.70   2.00 1.7662 49.3 17  −8.00 40.70 AIR 18  infinity 2.00 1.766249.3 19  −20.33   50.40 AIR 20  IMAGE PLANE EFL = −5.737 .017 N.A. 60DEG F.O.V. MAGN = .500

TABLE XII 1 2 3 4 5 6 7 8 9 10 11 12 FIG. N.A. FOV M EPD El. Relay sCDist Ptz WavFr AxClr 1 0.020 60 1.0 −0.5   3 1 1.62  −2 0.54 0.79 0.90 20.020 60 1.0 0.6 3 1 1.15  −2 0.40 0.32 0.80 3 0.020 60 1.0 6   3 1 0.55 −1 0.18 0.10 0.21 4 0.020 60 1.0 2   3 1 0.99  +2 0.20 0.27 0.31 50.015 70 1.0 0.2 5 1 0.84 −16 0.25 0.31 0.12 6 0.025 60 0.0 3.2 4 1 0.96 −3 0.23 0.46 0.14 7 0.020 70 1.0 1.9 4 I 0.72  −6 0.24 0.27 0.63 80.025 60 1.0 3.2 5 1 1.06  −1 0.19 0.21 0.31 9 0.025 60 2.0 2.4 5 1 1.47 +0 0.23 0.15 0.03 10  0.025 80 −0.5   0.1 7 2 1.03  −2 0.33 0.31 0.3511  0.017 60 0.5 0.1 9 3 1.51 −11 0.36 0.48 0.04 Column 1 Figure number.Column 2 Numerical aperture at the output focal plane. Column 3 Totalfield of view at the object side, in degrees. Column 4 Magnification.Column 5 Entrance pupil distance (air equivalent value), in mm. Column 6Number of elements with optical power. Column 7 Number of image relays.Column 8 Sum of the absolute values of all curvatures (i.e., the sum ofthe absolute values of the reciprocals of the radii of curvature), inunits of 1/mm. Column 9 Maximum image distortion in percent. Column 10Petzval sum of the total system, in units of 1/mm. Column 11Monochromatic peak to valley wavefront deformation over the whole fieldand unvignetted aperture. Column 12 Axial chromatic aberration in waves.

Having thus described the invention I claim:
 1. An optical endoscope forimaging using visible light including a plurality of optical elements,comprising: an objective; and a relay system, said relay system havingat least one optical element providing color correction for saidendoscope, said objective providing substantially no color correction,said objective and said relay system aligned along a common opticalaxis, wherein said optical elements include curved surfaces and thenumber of curved surfaces in said objective system and said relay systemtogether is not more than
 5. 2. The optical endoscope of claim 1,wherein the number of curved surfaces in said objective system and saidrelay system together is not more than
 4. 3. The optical endoscope ofclaim 1, wherein said objective system includes no more than 2 lenselements having optical power.
 4. The endoscope of claim 1, wherein saidendoscope includes not more than 9 lens elements having optical power.5. The endoscope of claim 4, wherein one of said optical elements is asinglet lens.
 6. The optical endoscope of claim 1, wherein saidobjective includes a singlet lens.
 7. The endoscope of claim 1, saidplurality of optical elements providing an axial chromatic aberration ofless than about 0.31 waves when the numerical aperture is 0.020.
 8. Theendoscope of claim 1, said plurality of optical elements providing amonochromatic wavefront deformation of less than about 0.27 waves whenthe numerical aperture is 0.020.